This invention relates to an apparatus and method for sealing two layers of a web of plastic material together. In particular, the present invention relates to an apparatus and method for forming the transverse seals in a web of film in a form, fill, and seal packaging machine.
Typically, form, fill, and seal packaging machines are utilized to package a product in flexible containers. To this end, form, fill, and seal packaging machines are utilized to seal pharmaceuticals, dairy products, wine, food stuffs, cosmetics and other products in flexible containers. The form, fill, and seal packaging machine provides an apparatus for packaging these products in an expedient manner.
In one type of form, fill, and seal packaging machine, a web of heat-sealable film is passed over a former or mandrel that forms the film into a tubular shape. To effect the tubular shape, the film is folded longitudinally and heat sealed along abutting longitudinal edges. The tubular shaped film is then passed around a tubular fill system that deposits the product to be packaged into the tubular shaped film. To create individual packages (hereinafter "bags") the web of film must be sealed across its width. These "transverse seals" function as a seal to form a pouch in the web of film for receiving the material to be packaged, and seal the filled end of a previously filled pouch. After the transverse seals are created, the web may then be severed into an individual bag.
The two usual methods of creating the transverse seals in a web of film are impulse sealing and constant hot bar sealing. Impulse sealing is a technique through which the energy required to heat seal the film together is delivered electrically in precisely measured pulsed charges. Usually, the measured electrical charge is pulsed through a ribbon of resistant metallic material for a predetermined time while the two layers of film are clamped together by jaws in intimate juxtaposition. The energy of the impulse sealer causes the film to soften and bond together. After the film is melted together, it must be cooled to a crystalline condition before the jaws may be opened or the film may separate.
Although the impulse system is effective for creating the transverse seals in a web of film, it requires a great deal of maintenance and utilizes certain consumable components. Accordingly, the production process must be periodically interrupted so that the consumable components may be replaced. One such consumable component is the ribbon element which has a relatively short life and must be replaced at regular intervals. The ribbon elements also include covers--the covers ensure that the melted film does not adhere to the ribbon element--that also have a relatively short life and must be constantly replaced.
In a production machine, replacing and changing these consumable elements can be a costly nuisance. Moreover, interruption of the form, fill, and seal procedure for routine maintenance is especially costly and time consuming in the case of an aseptic packaging system. Interruption of an aseptic production system not only means production interruption, but also necessitates the time consuming process of resterilization of the work area prior to restarting production.
Another method of creating the transverse seals in a form, fill, and seal packaging machine is to utilize a static or hot bar system. The hot bar system utilizes a sealing bar heated to an appropriate temperature by an electric cartridge heater. The sealing bar is then maintained at this temperature by the cartridge heater. The hot bar system suffers two major drawbacks. Because the sealing bar is constantly heated, it is difficult to precisely control the amount of energy, i.e. BTUs, that flow into the web of film while the layers of the web of film are in intimate contact. This is important because the portions of the film that are melted to create the transverse seals must be subsequently cooled to the point of crystallization before the film may be released and a new set of transverse seals created. Moreover, due to the constant heat, it is not possible to release the web of film, after creating the transverse seals, from the sealing jaws without the addition of some type of consumable or replaceable release element or the use of a slip arrangement.
Other methods of sealing a web of film in a form, fill, and seal packaging machine have been utilized, including ultrasonic welding, heated gas, and radiofrequency welding. While in special situations these techniques may be preferred, these methods of creating transverse seals in a web of film to create bags are expensive and slow.
Thus, there is a need for an apparatus and method for creating transverse seals in a form, fill, and seal packaging machine that overcomes the disadvantages of the prior art.